Motor randomly turning on

[_alice_]

I have foldable 20" ebike that has turned on it's motor randomly while I have been waiting for example green light. Last and final time caused my other arm to be unusable for few weeks, so I'm wanting to replace all risky electronics as otherwise the bike is decent.

With first incidents I thought I had accidentally somehow touched switch for walking assist (with it bike should go max to 6km/h) but I physically prevented that switch from moving afterwards - didn't fix the issue. I also think that the motor put much more power on than what it does when the assist goes on.

Last time the motor stopped only after I pressed brakes which luckily had been fixed just before as bike also had had the issue that pressing brake was not stopping the motor. On the same occasion motor turned back on when I released the brakes (I think maybe not immediately but not sure as I had crashed to ground pretty badly, so not too well in my senses back then).

Information of the bike:
* 36V
* Motor: Ningbo siwei motor JKXH36V250W20 1712110063
* Controller: KZQW22A-LKTS17066-8120, Suzhou Tongsheng bicycle Co. Ltd
* has one USB port up to 2.1A

What parts and sensors you think I should change? Or should it all be trashed? And being really noob with these: what would be the correct parts to buy?

Also, I would like to add rear light to it because it becomes now mandatory here by law. Do you think it would be possible to just add some light to the cable that goes to front light? Or is there risk to put too much load to the wire then?

PS: I did contact place where I got the bike and did get my money back on it AND to keep the bike. Now just I would prefer to fix it instead of trashing it as that would seem like waste of good parts.

 

[amberwolf]

The most likely problem is the ground wire in the throttle has a poor connection. It could be anywhere from the sensor inside the throttle itself all the way to where it solders to the board inside the controller. But the most likely place is at the connector between those, or where the wire exits the throttle housing itself.

If the ground wire (usually black) breaks, then the throttle voltage appears to the controller to jump up to full output, so the controller tries it's best to comply with the demand.

Also, I would like to add rear light to it because it becomes now mandatory here by law. Do you think it would be possible to just add some light to the cable that goes to front light? Or is there risk to put too much load to the wire then?

It's easiest to just get a light that has its' own battery, even if it's less convenient. This way you don't have to learn how all the wiring already on the bike works, then find a light that will work with that, etc.

 

[_alice_]

Thanks for your reply!

So, I should change the throttle and the controller with cables at least to be sure.

I just have to say that it is pretty scary that bad connection can make the bike act in this kind of manner (because of your post, I was able to find other people who have had this problem too...)

Is there any way to make sure the bike would be actually safe? And that motor would preferably stay OFF instead of ON in case there is any malfunctioning. And is this like feature of all electric bikes or just some? :?

 

[amberwolf]

Yes, I've had this problem myself but only when I was working on the SB Cruiser trike once, and did something that disconnected the ground but not the other wires.


If you don't want to actually find out where the problem is to just fix the problem, and would rather just swap parts out, then yes, the throttle and all wiring from it to the controller would have to be changed. The controller itself as well, if you can't verify the wiring from it's connector to the board inside it.



The simplest way you can make a throttle "safe" is to have a button you must hold while using the throttle, that without being held disables the system. If you already have an ebrake, then you could wire the button in parallel with that. Or you can use the button to disconnect the 5v to the throttle anytime it is not in use.

More complicatedly, you could design electronics to detect that the ground wire is intact, and disable the throttle signal to the controller if it fails. This would have to go inside the controller box itself, at the PCB point where the throttle wires connect, to make the most difference. Preferably with a little light on the outside to show you if it's engaged or not so you can figure out what went wrong easily.

But the controller itself simply has no way to tell whether the voltage coming in is because of the throttle sending it because you turned it, or becuause of a failure of the ground wire, or even a direct short in the wiring to some other signal wire.

There *are* controllers that have two throttle inputs, which might be able to be programmed / setup such that they won't respond to any input unless one of the throttle inputs goes up in voltage at the same rate the other one goes down in voltage. Then you would build a throttle that has two sensors in it, and two sets of magnets, so that as you turn it the first one goes up in voltage, and the other goes down. If either one fails, the system will not engage, because it requires both to operate.

Some of the large EV controller systems already do this, but there's nothing for ebikes that does it without user-engineering of the system.